Children who don't master the basics of literacy (e.g. phonological awareness, alphabetic awareness and letter writing, vocabulary and oral language) in preschool risk failure in acquiring conventional reading skills later in elementary school (National Early Literacy Panel, 2008; Storch et al., 2002). Considering that Head Start (HS) largely serves children from minority or English?learning backgrounds, these children are particularly impacted (Head Start Program Facts, 2014). Development of early literacy skills depends on teacher preparation and readiness to teach those skills (Burchinal et al., 2009; Diamond & Powell, 2011). Pre?K teachers require focused training to improve knowledge about the high?priority skill targets in language and literacy development (Odom, 2008; Landry et al., 2006; Wasik et al., 2006). Findings show that HS teachers vary widely in their training and expertise with implementing evidence?based practices (Hart & Schumacker, 2005). To date, HS has had only minimal effect on children's literacy preparation (Whitehurst & Massetti, 2004), and the small literacy gains made by HS children do not maintain in kindergarten (DHHS, 2010). The persistent achievement gap between HS children and their peers, makes high?quality professional development vital-and efficient training and coaching even more so. We propose to develop a mobile application to assist teachers' mastery of language and literacy instruction. This technology?assisted approach will use an interactive e?checklist framework to operationalize fundamental instructional competencies, deliver video?based training and modeling on these competencies, and facilitate individualized in?class coaching by enabling teachers to meet with coaches via teleconference and receive feedback on video uploads of their teaching. Our approach stands in contrast to the costly one-size?fits?all training model currently available to HS teachers. To evaluate our approach, we will conduct an RCT randomly assigning 30 classrooms to either an intervention (Pre?K LiteracyCheck), or business?as?usual (BAU) control group (typical language and literacy professional development). Using standardized measures and in?class observations, this RCT will test the following hypotheses: (a) intervention group teachers will improve instructional competencies, (b) children of intervention teachers will demonstrate greater growth in language, literacy, and social skills than children in the BAU, c) English?learner children of intervention teachers will demonstrate greater growth in language, literacy, and behavioral skills than children in the BAU group, and d) HS teachers in the intervention group will report higher rates of self?efficacy than teachers in the BAU group, and report a high level of consumer satisfaction with Pre?K LiteracyCheck.